Various protocols used for biological or chemical research include the execution of a large number of controlled reactions. The reactions may be carried out in accordance with a predetermined protocol by automated systems that have, for example, suitable fluidics, optics, and electronics. The systems may be used, for example, to generate a biological or chemical product for subsequent use or to analyze a sample to detect certain properties/characteristics of the sample. When analyzing a sample in some cases, a chemical moiety that includes an identifiable label (e.g., fluorescent label) may be delivered to a chamber where the sample is located and selectively bind to another chemical moiety of the sample. These chemical reactions may be observed or confirmed by exciting the labels with radiation and detecting light emissions from the labels. Such light emissions may also be provided through other means, such as chemiluminescence.
Some known systems use a fluidic device, such as a flowcell, that includes a flow channel (e.g., interior chamber) defined by one or more interior surfaces of the flowcell. The reactions may be carried out along the interior surfaces. The flowcell is typically positioned proximate to an optical assembly that includes a device for imaging the sample within the flow channel. The optical assembly may include an objective lens and/or a solid state imaging device (e.g., CCD or CMOS). In some cases, an objective lens is not used and the solid state imaging device is positioned immediately adjacent to the flowcell for imaging the flow channel.
Before imaging the flow channel, it may be necessary to conduct a number of reactions with the sample. For example, in one sequencing-by-synthesis (SBS) technique, one or more surfaces of the flow channel have arrays of nucleic acid clusters (e.g., clonal amplicons) that are formed through bridge PCR. After generating the clusters, the nucleic acids are “linearized” to provide single stranded DNA (sstDNA). To complete a cycle of sequencing, a number of reaction components are flowed into the flow channel according to a predetermined schedule. For example, each sequencing cycle includes flowing one or more nucleotides (e.g., A, T, G, C) into the flow channel for extending the sstDNA by a single base. A reversible terminator attached to the nucleotides may ensure that only a single nucleotide is incorporated by the sstDNA per cycle. Each nucleotide has a unique fluorescent label that emits a color when excited (e.g., red, green, blue, and the like) that is used to detect the corresponding nucleotide. With the newly-incorporated nucleotides, an image of numerous clusters is taken in four channels (i.e., one for each fluorescent label). After imaging, another reaction component is flowed into the flow channel to chemically cleave the fluorescent label and the reversible terminator from the sstDNA. The sstDNA is then ready for another cycle. Accordingly, a number of different reaction components are provided to the flow channel for each cycle. A single sequencing session may include numerous cycles, such as 100, 300, or more.
The fluids that include the reaction components are typically held in a storage device (e.g., tray or cartridge) in which different fluids are stored in different reservoirs. Due to the number of reaction components and the large number of cycles, the total volume of fluid that is used during one session can be quite large. In fact, for some applications, it is impractical to supply the total volume of reaction components in a single cartridge. For such applications, it may be necessary to use a larger system, multiple systems, or to execute numerous sessions with a single system. These solutions can be costly, inconvenient, or unreasonable in some circumstances.